1. Technical Field
The present invention relates to a printing apparatus.
2. Related Art
A printing apparatus in the related art includes a transport unit that transports a medium such as a sheet and a printing unit that has a print head which performs printing on the medium transported by the transport unit. The transport unit has a transport roller which transports the medium, a feed motor that rotates the transport roller, and a detection unit which detects a transport amount of the medium.
When the medium is transported by the transport roller, slippage occurs between the medium and the transport roller in some cases. In a case where such slippage occurs, the transport amount of the medium with respect to a rotation amount of the transport roller varies from a transport amount of the medium with respect to a rotation amount of the transport roller which is obtained when there is no slippage between the medium and the transport roller. In order to stop the variation, the printing apparatus in the related art controls the transport amount of the medium by a feedback control which causes a detection amount which is the transport amount of the medium which is detected by the detection unit to be approximate to a theoretical transport amount which is a transport amount on design in a case where the medium is transported by one pulse drive of the feed motor.
In a case where the detection unit outputs a detection amount which is significantly different from an actual transport amount, that is, a case where the detection unit detects an abnormal value as the detection amount, the printing apparatus in the related art controls the transport amount of the medium based on the abnormal value, and thus, transport of the medium is performed inaccurately.
In regards to such a problem, JP-A-2003-267591 discloses a printing apparatus (image forming apparatus) that sets a normal range in advance with a theoretical transport amount as a reference and controls a transport amount of a medium based on a predetermined specified transport amount instead of a detection amount when the detection amount is not within the normal range, that is, the detection amount is an abnormal value. Accordingly, since the abnormal value is not used as a value used to control the transport amount of the medium, inaccurate transport of the medium is prevented. The specified transport amount is a preset fixed value.
Incidentally, it is technologically difficult to manufacture a perfectly-circular circumferential shape of the transport roller which is a cross-sectional shape orthogonal to an axial direction thereof. Therefore, the rotation amount of the transport roller by one pulse drive of the feed motor varies depending on a rotation position of the transport roller in some cases. Thus, the transport amount of the medium through the rotation of the transport roller by the one pulse drive of the feed motor varies depending on a rotation position of the transport roller in some cases. In addition, a slippage amount between the medium and the transport roller varies depending on the types of media (types of sheets) in some cases.
In the printing apparatus in the related art, the specified transport amount is a fixed value and a slippage amount between the medium and the transport roller, the variation of the slippage amount depending on the types of media (types of sheets), or the variation of the transport amount depending on the circumferential shape of the transport roller is not reflected in the specified transport amount. Therefore, there is a concern that inaccurate transport of the medium is performed even by controlling the transport amount of the medium based on the specified transport amount, and thus, there is still room for improvement.